A frame transfer CCD image sensor in general includes three sections: a photosensing array, known as the A-register; a temporary storage array, known as the B-register; and an output register, known as the C-register. The three registers are formed along a major surface of a substrate of semiconductor material. It is the practice to mask out the B-register and the C-register so that light from the image being sensed will only impinge upon the A-register. In one type of CCD image sensor the light enters the semiconductor substrate through its surface opposite to the surface along which the registers are formed, which surface is generally referred to as the back surface of the substrate. In order to allow the light to pass readily through the substrate to the A-register, the substrate is thinned from its back surface and a glass plate is mounted on the back surface to provide support for the thin substrate. This type of device is described in U.S. Pat. No. 4,266,334 to T. W. Edwards et al., issued May 12, 1981, entitled "Manufacture of Thinned Substrate Imagers". In this type of imager the mask for the B-register and C-register is a metal film coated on the surface of the glass plate. To apply the masking film to the glass plate, an apparatus is required which will hold the imager and a mask and will allow proper alignment of the mask and the imager.